A touch panel or touch screen is one of the major interfaces between human and machine, and as a recognition device, can ingeniously combine input and display interfaces, and therefore has the advantages of saving device space and user-friendly operation. Nowadays it has been generally applied to a wide variety of consuming or industrial electronic products. For example, PDAs (Personal Digital Assistant), palm-sized PCs (Personal Computers), tablet computers, mobile phones, handwriting input devices for a smart phone, IAs (Information Appliances), ATMs (Automated Teller Machines) and POS (Points-of-Sale), etc., which can generally be seen in various occasions of business and industry applications.
Especially when the projected capacitive (PCI or PCAP) touch technology integrated in said electronic products, no matter that the outdoor or portable PCI electronic products may come into contact with liquid such as rain or spilled beverages. For example, the new treadmill incorporate PCI touch panels, runners' sweat will contaminate the touch surface; PCI systems used on oceangoing vessels may be splashed with seawater; or, PCI touch panels utilized in the medial field will have to endure saline, blood, and other liquids.
One of the challenges frequently encountered by PCI touch panel applications is the difficulty of obtaining a reliable object signal (touch signal) when liquid is present on the touch surface. Projected capacitive touch sensing relies on the interpretation of minute changes in electromagnetic fields projected by capacitors embedded in the touch surface caused by the interaction of conductors such as a finger or a touch pen with these fields. Therefore, water, dishwashing liquid, saline (0.9% NaCl), blood (0.9% salinity), and even saltwater (3.5% salinity), which are conductor, will cause false touch signals when present on the touch surface. How to effectively determine the false touch signal caused by liquid from interfering the object identification result is the most important issue in touch technology.